Binding of ligands (carbon monoxide, oxygen, nitric oxide) to heme proteins and heme model compounds is investigated by means of flash photolysis. After photodissociation by a laser pulse of 1 microns duration, changes in optical absorbance are monitored from 2 microns to 1 ks. The temperature is varied from 2 to 350 kelvin. Pressures up to 5 kbar can be applied in the temperature range above about 20 K. BIBLIOGRAPHIC REFERENCES: H. Frauenfelder, Dynamik der Biomolekule, Physikalische Blatter 31, 627-634 (1975). R.H. Austin, K.W. Beeson, L. Eisenstein, H. Frauenfelder, and I.C. Gunsalus, Dynamics of Ligand Binding to Myoglobin, Biochemistry 14, 5355-5373 (1975).